Method and apparatus for measuring small displacements



Dec. 31 1935 L. w. BLAU ET AL. 2,025,719

METHOD AND APPARATUS FOR MEASURING SMALL DISPLACEMENTS Filed Ndv. 21. 1930 waw w I :PatentedDec. stress v s 1 2,025,719

UNITED STATES PATENT o icE Mn'rnon APPARATUS Fort MEASURING SMALL nrsrmcsmm'rs Ludwig W. Blau, Andrew B. Bryan, and Whitman D. Mounce, Houston, Tex., assignors to'Standard Oil Development Company, a corporation of Delaware I Application November 21, 1930, Serial No. 497,104

' 1 8Claims.- (01. 177-350,.

This invention relatestoimprovementsinmethbatteries for operating the vacuum tube are in: ads and apparatus for the mt or 'indidicated at-ll and i8. cation oi small spatial displacements -by varia- It will 'be understood that other equivalent tion in the capacity of an electrical system; In means may be substituted for the four element accordance with the invention, the displacement vacuum tube shown, for example a three-elec- 5 to be measured or indicated is caused to move trode tube. a i L one set of condenser plates with'respect to an- Thetin terior plates 2, 3 of the double'condenserother set of such plates. The resulting changes are connected bya lead 19 withthe. vacuum tube in capacity are caused to produce a suitable sig circuit, and the exterior plates 4, 5 are connected hal. a v with the plate and grid'portions of that 'circuit 10 The displacementmay bea minute expansion by leads ,20 and 2|,respectively'." The support or contraction, as in the determination of the carrying plates 2 and'3 isuiade of a suitable coemcient 0! thermal expansion of a solid or the electrically conductive materihl. volumetric changes of liquids and gases; or the In Fig. 2 is shown a microphone diaphragm, l5 displacement may be a vibration caused by connected by a rod 23 with a condenser plate 24. sound waves acting on the diaphragmof a micro- This latter is arranged between condenser plates phone, or the like. Owing to the extreme sensi- 25 and 23 which are mounted in fixed position. tiveness or the present instrument, a particular- Plate 2 i o n d wi the va u e cir-, ly advantageous use is in the study of earthcuit by lead is as in Fig. l. Plates 25 and 26 quakes, either natural or such as are. produced are connected r p v wi that circuit by- ,as an incidentxto geophysical exploration, The leads -20 and 2|. f 5/ suggested uses are illustrative and'others will be In Fig. 3, 21 illustrates the exnans le memapparent to those skilled in this art. v ber of i a thermal expansion measuring instru- The invention will be fully understood from m nt- Pivctal y u t d o t e p of t s Q5 the following description read in connection-with member is a rod 23 carrying a condenser ele- 25 the accompanying drawinginwhich ment 29. Condenser platesffll and 3| are ar- Fig. '1 is a diagram showing the electrical sysranged in opposed relation to the element 29. tem, and Connection to the vacuum tube circuit is made as Figs. 2, 3, and 4 are side elevations showing the described above. 80 various means for causing movement of the con- Fig. 4 illustrates the use 0! the intention in denser plates. connection with the seismograph. The suspended Referring first to Fig. 1, reference numeral l weight member 32 of this instrument carries condenotes a movably mounted support carrying denser plates 33 and 34 arranged interiorly with condenser plates 2 and 3. These are arranged respect to condenser plates 35 and 36. Vibra- 85 in opposition to rigidly mounted condenserplates tory motion of the weight member varies the 35 4 and 5. In the double condenser thus termed capacity of the double condenser thus formed. movementof support I either to the right or left The changes in capacity sire impressed on the re ul s in a corr p ndin in rease r decrease vacuum tube circuit by connection, with it respectively in the capacity of condensers 2, 4 and through the leads shown.

v 1 The operation of the present invention in any 40 In the preferred form of the invention illusof the foregoing embodiments is as follows: m the 11185118 r mm h variation of The capacities of the condensers 2, 4 and 3 5 08081315748 5 Viwuu tube (lildion) circuit emfor example are preferably made substantially 9 M 8: m element ub ch as a screen grid equal when they are in their equilibrium positube- In W e vac u t e is shown .diation, but such equality is not essential. Then the 5 am ic y with o d p e Va iab circuit is tuned by means of the condenser-' 8 or condensers 8 n 9 r n th ri c r uit a h 9 or both. Condenser it acts as a feed-back. pla circuit respectively of t vacuum be A When the circuit has been tuned'it is very sensivariable condenser I! is in a bridge between the tive to changes in the capacity oi the double grid and plate circuits. Aninductance II is arcondenser system. Even extremely minute (115- so ranged in the plate circuit'and an inductance l2 placements of the interior plates with respect in the grid circuit. Agrid battery l3 and'blocke to the outer plates cause a variation in the plate 7 ing condenser I4 are supplied as usual. Also current sufficient to make a readily'perceptible the radio irequo'ncychoke I! and output transindication. This indication maybe audible as former It my boot the conventional type. The through ear phones, or it may be visual as by the interposition of oscillographic means and the like. Suitable provision for recording the indications can be made if desired in known manner. Any desired amplification can be obtained by the use of additional amplifying means. The evaluation and interpretation of the indications can be made in ways well understood in the art.

It has heretofore been proposed to determine displacements by causing the same to vary a condenser capacity acting on the grid circuit of determining displacements. This is to be understood as meaning not only the physical extent of the displacement but also the inferences and deductions that can be made from a study of the indications obtained, and the uses that result therefrom. As an example of the latter, mention is made of microphone reproduction for broad casting.

While interior condenser plates movably mounted have been shown, itiis obvious that these may be stationary and the outer plates movable. Various other changes and alternative arrangements may be made within the scope 'of the appended claims, in which it is intended to claim all novelty inherent ,in the invention as broadly as the prior art permits. i

We claim:

1. Method of determininga minute displacement, comprising energizing a vacuum tube circuit including grid and plate circuits, tuning the circuits, causing such displacement to change the capacity of condensers simultaneously and oppo-' sitely, impressing such-changes respectively on the grid circuit and the plate circuit of the vacuum tube, and determining the extent of displacement from. the resultingwariation in the current output of the electrical system.

2. In combination with an electrical circuit in-' cluding a vacuum tube having a grid' circuit and a plate circuit, means for tuning the circuits, a

plurality of sets or relatively movable condenser elements connected 'to constitute a double condenser, a body capable of displacement and connected with said condensers so 'as to change their capacity simultaneously and oppositely due to the displacement to upset the plate current, and means for impressing the changes of capacity upon the said grid and platecircuits respectively.

capacities of the condensers simultaneously and in opposite directions to change the current of the plate circuit.

5. In an electrical circuit including ;a three element tube having a plate circuit and a grid circuit, a variable condenser in the grid circuit and a variable condenser in the plate'circuit for controlling the-plate current, a condenser con- .nected in the circuit with the plate oi said tube, acondenser connected in the circuit with the grid of the tube, and means for varying the capacities of the condensers simultaneously and in opposite directions to change the controlled current of the plate circuit.

6. In an electrical circuit including a three element tube having a plate circuit and a grid circult,- means for tuning the circuits, a condenser connected in the circuit with the plate of said tube, a condenser connected in the circuit with the grid of the tube, means for varyingthe capacities of the condensers simultaneously and in opposite directions to change the current of the plate circuit, and a bridge between the grid and plate circuits.

7. In an electrical circuit, a vacuum tube having a plate circuit and a grid circuit, means for tuning the circuits and a variable double condenser including spaced outer electrically conductive plates, a unit including inner electrically conductive plates mounted for movement toward and from the outer plates, a vibratory member rigidly connected to the unit whereby vibrations oi the member vary the capacities of the condensers simultaneously and in opposite directions to upset the plate current, means for grounding the inner plates, the outer plates being in the plateand grid circuits respectively.

8. In an electrical'circuit, a vacuum tube hav vibrations of the member vary the capacities of the condensers simultaneously and in opposite directions to change the current of the plate circuit, means forgrounding the plates of one unit, the plates 01' the other unit being in the plate and grid circuits respectively.

9. In an electrical circuit including a three element tube having a plate circuit and a grid circuit, means for tuning the circuits, a condenser connected-in the circuitwith the plate of said tube, a condenser connected in the circuit with the grid of said. tube, and a microphone diaphragm operatively associated with the condensers to vary the capacities of the condensers simultaneously and in opposite directions to change the current of the plate circuit upon vibration ot the diaphragm.

.10. In an, electrical circuit, a vacuum tube having a plate circuit and a grid circuit, means for tuning the circuits, and a variable double-condenser including -a unit comprising spaced outer electrically conductive plates, a second unit including an inner electrically conductive plate, a microphone diaphragm associated with one of the units whereby vibrations" of the diaphragm vary the capacities, of the condensers simultaneously and in opposite directions to change the current, of the plate circuit, and means for grounding one 01' the units, the plates 'pi the other unit being in the plate and grid circuits respectively. I I

11. In an electrical circuit, a vacuum 'tube hav- -ing.a plate circuit and a grid circuit, means for tuning the circuits, and a variable double condenser including spaced outer electrically con- 'ductive plates, an inner electrically conductive plate mounted for movement toward and from the outer plates, a microphone diaphragm connected to the inner plate whereby vibrations of tube, a condenser connected in the circuit with the diaphragm vary the capacities of the condensers simultaneously and in opposite directions to upset the plate current, and means for grounding the inner plate, the outer plates being in the plate and grid circuits respectively.

12. In an electrical circuit including a three element tube having a plate circuit and a grid circuit, means for tuning the circuits, a condenser connected in the circuit with the plate of said tube, a condenser connected in the circuit with the grid of said tube, anda seismograph including a mass resiliently suspended from a frame, the mass and frame being operatively ascluding a unithaving spaced outer electrically conductive plates, and a unit including innerelectrically conductive plates, a seismograph including a mass resiliently suspended from a frame, means connecting the mass to the plates of one of the unit's, means connecting the frame to the plates of the other unit whereby vibrations of r the frame vary the capacities of the condensers simultaneously and in opposite directions to change the current of the plate circuit, means for grounding the plates of one of the units, the plates of the other unit being in the plate and grid circuits.

14. In an electrical circuit, a vacuum tube having a plate circuit and a grid circuit, means for tuning the circuits, and a variable condenser including spaced outereiectrically conductive plates and an inner electrically conductive plate mounted for movement toward and from the outer plates, and a seismograph including a mass resilientiy suspended from a frame, the mass being rigidly connected to the inner plate and the frame being connected to the outer plates .whereby vibrations of the frame vary the capacities of the condensers simultaneously and in opposite directions to upset the plate current, the inner plate being grounded, the outer plates being in the plate and grid circuits respectively.

15. In an electrical circuit including a three element tube having a plate circuit and a gridthe grid of said tube, and an expansible member operatively associated with the condensers to vary the capacities of the condensers simultaneously and in opposite directions to change the current 5 of the plate circuit upon movement of the ex-.. pansible member. a 4

16; In an electrical circuit, avacu'um tube having a plate circuit and a grid circuit, means for tuning the circuits, and a variable double condenser including spaced outer electrically conductive plates, an inner electrically conductive plate mounted for movement toward and from the outer plates, and an expansible member rigidly connected to the inner plate whereby movement of the expansible member varies the ca- 1 pacities of the condensers simultaneously and in opposite directions to upset the plate current, means for grounding the inner plate, the outer plates being in the plate and grid circuits respectively.

17. In an electrical circuit including a, three element tube having a plate circuit and a grid circuit, a variable condenser and an inductance in the plate circuit for obtaining resonance of -33 high frequencies in 'the plate circuit, a variable condenser and an inductance in the grid circuit for obtaining resonance of high frequencies in the grid circuit, a condenser connected in the circuit with the plate of said tube, a condenser :33 connected in the circuit with the grid of the tube, and means for varying the capacities of the condensers simultaneously and in'opposite directions to change the current of the plate circuit.

18. In an electrical circuit including a three 35 condenser a'n'dan inductance in the grid circuit 40 I I for obtaining resonance of high frequencies in the grid circuit, a condenser, connected in the circuit with the plate of said tube, a condenser connected in'the circuit with the grid of the tube, and a microphone diaphragm. operatively associated with the condensers to varywthe capacities of the condensers simultaneously and in opposite directions to change the current of the plate circuit upon vibration of the diaphragm.

' LUDWIG W BLAU.

ANDREW B. BRYAN. WHITMAN D. MOUNCE. 

